


A Rainbow of Bones

by ArgentDandelion



Category: Undertale (Video Game)
Genre: Analysis, Archaeology, Art, Biology, Forensics, Gen, Nonfiction, Paleontology, Science, Skeletons, Taphonomy, Taxidermy, Weird Biology, character design
Language: English
Status: Completed
Published: 2019-08-08
Updated: 2019-08-08
Packaged: 2020-08-13 01:30:02
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 5
Words: 3,016
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20165902
Author URL: https://archiveofourown.org/users/ArgentDandelion/pseuds/ArgentDandelion
Summary: Covers the variety of colors real-life skeletons can come in, whether naturally, by decay, by fossilization, by cooking or by contaminants or poison. Though it focuses on how to make creative Undertale skeleton-monster original characters which don't look just like Sans and Papyrus, it's applicable to any skeleton characters.





	1. Introduction and Most Common Colors

  
(**Left**: Art from _[The Anomaly](http://anomalouscomic.tumblr.com/index)_, by [Coffeelemental](http://coffeelemental.tumblr.com/). **Right**: Art from the “[Ukagaster](http://zarla-s.tumblr.com/post/180501498387/so-today-is-the-third-anniversary-of-handplates)” application, by [Zarla](http://zarla-s.tumblr.com/).)

  


* * *

#  **Introduction**

In-game, Papyrus and Sans have the same bone color: pure white. Yet, it’s a common fan trend to give them slightly different bone colors, with Sans’ bones often being bluish-white and Papyrus’s bones being orange-ish white.[1](https://argentdandelion.tumblr.com/post/181029039127/a-rainbow-of-bones-resource-on-skeleton-monster#fn:1)

Initially, I considered this trend odd and implausible. They are brothers; why should their bones be so drastically different in color? But then I remembered: though brothers, they are practically physical opposites, representing two very different ways to draw skeletons.  
If even two brothers can physically differ so much, it’s likely skeleton monsters as a whole have great physical diversity, perhaps including bone color. After all, there are plenty of samples of monster breeds having drastically different colors, with Snowdin’s especially colorful bunny monsters being a good example.

* * *

#  **Most Common Colors**

**White/Light Grey**

  
Their bones’ color is exactly the same as Microsoft Paint’s background color.

Bones get their white color from hydroxyapatite (calcium phosphate), their primary mineral component. However, bones aren’t pure chalk-white straight out of the human body. Skeletons used for [display](https://t.umblr.com/redirect?z=https%3A%2F%2Flifehacker.com%2Fhow-to-clean-animal-bones-so-that-you-may-proudly-displ-1798191351&t=MzUzOWZkZjFkMjkzZTEyMGQ1MDNmY2U5NDA2NWRhYzE2ODdiYmU4ZSxObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) (if they aren’t plastic imitations) are first “bleached” (actual bleach dissolves bones) with cleaning and chemical treatment, eventually leading to the familiar white/beige color.

Bones change color naturally, too. Originally yellowish/pinkish (see later entries), once soft tissues are removed, they begin to [dehydrate](https://t.umblr.com/redirect?z=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D6zMlDwAAQBAJ%26lpg%3DPA79%26ots%3DMQUrw6IZpa%26dq%3Dbones%2520change%2520%2522color%2522%2520with%2520age%252C%2520yellow%26pg%3DPA79%23v%3Donepage%26q%26f%3Dfalse&t=YmE3MmVjNDUzOGNlNDEyNThlOWE1MjY4MmViOWM1NThmZTdjM2I4MixObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) and take on an ivory (off-white) color. However, over time, bones may change color again according to environmental factors. For example, in strong sunlight, bones are naturally “bleached” via the UV light in sunlight, and eventually turn grey this way.[2](https://argentdandelion.tumblr.com/post/181029039127/a-rainbow-of-bones-resource-on-skeleton-monster#fn:2)

Strangely enough, bones also turn white in fire. Initially, burning bones blackens them, as one would expect, but as the internal temperature rises, the color changes: according to one source, the order after that is grey, then bluish-grey, then finally white.[3](https://argentdandelion.tumblr.com/post/181029039127/a-rainbow-of-bones-resource-on-skeleton-monster#fn:3) At this stage, they are said to be “calcined”, and look very similar to UV-bleached bones.

**Yellow/Yellowish**

It’s fairly common for cartoon skeletons to be yellow. Bones, indeed, can be yellow/yellowish, though cartoons often exaggerate this. To be specific, normal fresh bone with no flesh has been described as having a yellowish-white to yellowish-brown color, due to lipids (fatty/oily chemicals) and other fluids.

[Some](https://t.umblr.com/redirect?z=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D6zMlDwAAQBAJ%26lpg%3DPA79%26dq%3Dbones%2520change%2520%2522color%2522%2520with%2520age%252C%2520yellow%26pg%3DPA372%23v%3Donepage%26q%26f%3Dfalse&t=MWJiMTEzNDM5NmM1YTViNTI5MGM3MTliMTMxODg4OGFjYmM2ODAyOCxObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) [sources](https://t.umblr.com/redirect?z=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DGmGZCwAAQBAJ%26lpg%3DPA86%26ots%3DnIeVz0tvmJ%26dq%3Dpugilistic%2520pose%252C%2520skeletons%252C%2520yellow%252C%2520heat%252C%2520brown%252C%2520black%252C%2520grey%252C%2520white%26pg%3DPA86%23v%3Donepage%26q%26f%3Dfalse&t=ZDY3YjQ0MjU0NDA3MWNhZmU3YzZmYjNmNTI5MTczNTJhOWI3ZTRlMSxObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) note that bones are yellow or yellowish when exposed to high temperatures. It’s possible that, if the temperature’s low enough, the bones don’t change from the natural yellowish color they have when freshly removed from a body.

Certain drugs and poisons [can turn bones yellow.](https://t.umblr.com/redirect?z=http%3A%2F%2Fwww.rosincerate.com%2F2015%2F10%2Fweird-colours-of-bones-and-teeth.html&t=MWQyNGRhZDc0MDgyOTk0YzQ1YTUxNTlkYWU4OWRjNDJlYTE4NTJkYixObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) One of the most common examples are the drugs tetracycline and minocyline, which can change the color of bones (including teeth) to a variety of shades, yellow included. This isn’t just a quirky modern thing: this phenomenon has been discovered in skeletons of ancient Egypt and Sudan, with one possible explanation those populations ate food contaminated with tetracycline-producing bacteria.

It is [suspected](https://t.umblr.com/redirect?z=https%3A%2F%2Fjamanetwork.com%2Fjournals%2Fjamaophthalmology%2Ffullarticle%2F419116&t=MzdkNjNiY2VlZTdhOWRhMzkxOWJkM2NkNmMwYzAzNjU4Y2UzZDE4ZSxObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) carotene (found in foods such as sweet potatoes and carrots) can color bones yellow, but this has never been proven.

Interestingly, there’s [a correlation](https://t.umblr.com/redirect?z=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DdQfSBQAAQBAJ%26lpg%3DPA316%26vq%3Dincreased%2520yellow%2520hue%26pg%3DPA316%23v%3Dsnippet%26q%3Dincreased%2520yellow%2520hue%26f%3Dfalse&t=NGQyZTlkM2YxOTQ1Y2E0MWY4YjIyNTNkYjU1OTEwNTBiOGM5MGEzNSxObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) between increased yellow hue in the skull and increased age at death; this fun fact might come in handy for distinguishing elderly skeleton monsters. (assuming they’re based on human skeletons)

* * *

  1. (This is [likely](https://undertalethingems.tumblr.com/post/180734432136/while-working-on-a-post-on-potential-different) because it makes things more interesting or is easier to shade than pure white.) [↩︎](https://argentdandelion.tumblr.com/post/181029039127/a-rainbow-of-bones-resource-on-skeleton-monster#fnref:1)

  2. So, theoretically, a fire monster/skeleton hybrid might have bright white bones from fire, or greyish-brown bones, dark grey bones, bluish-grey bones, black bones, or yellow bones, or various other colors. That’s if one isn’t considering the possibility not all off the body is on fire or that flames on different parts of the body have different temperatures, leading to multiple colors. Apparently, a skeleton on fire can practically be a rainbow.  [↩︎](https://argentdandelion.tumblr.com/post/181029039127/a-rainbow-of-bones-resource-on-skeleton-monster#fnref:2)

  3. Someone even wrote [a story](https://t.umblr.com/redirect?z=https%3A%2F%2Farchiveofourown.org%2Fworks%2F15762315&t=MWE1OTI3NjUwYmM1OWZjNWNlNGU3NzUxOTUxZGY0M2NmNWI1NmNlZixObkFMc1lOcA%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181029039127%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) that related bone bleaching to getting a tan. [↩︎](https://argentdandelion.tumblr.com/post/181029039127/a-rainbow-of-bones-resource-on-skeleton-monster#fnref:3)


	2. Brown and Black

From left to right, clockwise: [black bone syndrome](https://t.umblr.com/redirect?z=http%3A%2F%2Fwww.scielo.br%2Fscielo.php%3Fscript%3Dsci_arttext%26pid%3DS1516-635X2013000400005&t=NmIzMTc4OTM0OWM3YWM1Yjk4NDUyNTg5ZDlkYjk3OGQ5YzA4ZjEwOCxoV3BKSUI4Mw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181230179984%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) in cooked chicken, two charred bone samples, [purple-black](https://t.umblr.com/redirect?z=https%3A%2F%2Fwww.hindawi.com%2Fjournals%2Fjanthro%2F2016%2F9479051%2F&t=ZmI2YWYxMTI3YjY2ZDJhM2IyNzhiMzVmZjY0MDdjNzY1MjcyNGY3MSxoV3BKSUI4Mw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181230179984%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) archaeological bone, one of Black Beauty’s bones, and a macerated animal bone.   
_(Note: This post is gore-free, but some of the linked pages are pretty gross.)_

* * *

#  **Brown and Black**

**Brown Bones**

While not well-represented in cartoons, video games, and stock images, these are all pretty common colors for skeletons, human skeletons included. Most archaeological/forensic skeletons are some shade of brown, but dark brown (close to black) and black are also fairly common in these contexts.

Normal, fresh bone without flesh has been described as yellowish brown (or yellowish-white; see previous post). Bones can also have brown (or black; see below) coloration from charring. It’s very common for forensic/archaeological skeletons to be some shade of brown. Acids in the soil, soil staining, iron, and decomposing plants are some common causes.

* * *

**Black Bones**

For all his mystery, W.D. Gaster is a common character in _Undertale_ fan works. Based on the assumption the Mysteryman sprite is W.D. Gaster, he’s often regarded as a skeleton monster, even a relative of Sans and Papyrus.

The Mysteryman sprite has a secret: if flipped upside-down, it shows another face, with white eyes on a black background. [Blookerton](https://blookerton.tumblr.com/post/175993519427/blookerton-this-here-isss-retsag-can-be-retsig) brought up the idea of a skeleton character with black coloration based on this, named “Retsag”.

**Biology**

While the user’s Retsag interpretation actually has white bones covered with a black substance, black bones really do exist. In some cases, it’s a natural phenomenon in living things. Though living humans only have black bones when they have the genetic disorder alkaptonuria, (don’t look for images if you’re squeamish) in two breeds of chickens, black bones are the norm. These breeds, the Silkie and Ayam Cemani, don’t just have black bones, but black skin, muscles, and organs. This comes from a condition called melanism, the reverse of the better-known albinism.

**Cooked**

Speaking of chickens, meat-eating readers are probably familiar with one cause of black bones: black bone syndrome. This harmless phenomenon happens when bone marrow leaks out from the bones of young chickens. When the chicken is cooked, the material turns dark, making reddish-brown or black coloration on the surface of the bones.

Obviously, bones can turn grey or black from simple cooking, and bones turn black when charred. However, bones can also gradually turn from brown to black if sealed in [modified-atmosphere packaging](https://t.umblr.com/redirect?z=https%3A%2F%2Fwww.researchgate.net%2Fpublication%2F45449096_Effects_of_packaging_on_bone_marrow_discoloration_in_beef_arm_rib_shoulder_blade_and_thoracic_vertebra_bones&t=MDc4OGVhMDVmNTEzMjZhOWFhMDI4NjFjNTUyYmNhMWQ3MWI2MTk4YyxoV3BKSUI4Mw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181230179984%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1). (essentially, bone-in meat sealed in a very high-oxygen atmosphere)

**Rotting**

Bones can also turn black [from rotting](https://t.umblr.com/redirect?z=http%3A%2F%2Fbone-lust.blogspot.com%2F2015%2F05%2Fbonelust-q-ive-been-macerating-bones.html&t=N2NlMjljYjgzOTg3N2E0Y2Q3YmZiNjZhMGQzYzliZjM2MTAzOGMwNyxoV3BKSUI4Mw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181230179984%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1).[1](https://argentdandelion.tumblr.com/post/181230179984/a-rainbow-of-bones-resource-on-skeleton-monster#fn:1) Those who make taxidermied skeletons might note that, under maceration (a taxidermy technique), their prepared bones might be covered in a black film. (A bit like StealthNerd’s Retsag design, actually)

**Minerals and Fossils**

Black bones are pretty common in archaeology and forensics. Several minerals and other substances, such as manganese dioxide and oxide, manganese carbonate, graphite, asphalt and [bitumen](https://t.umblr.com/redirect?z=https%3A%2F%2Fbonesdontlie.wordpress.com%2F2011%2F10%2F06%2Fcolored-bones-varied-meanings%2F&t=MDU2YTI1YWFjY2MzMDQ2Y2EzOTVhOWY2MzczNWQxZTZjN2Y3Nzg2ZixoV3BKSUI4Mw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181230179984%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) (the last often used to make mummies) can color human skeletons black. In a forensic sense, decomposing roots and [humic acids](https://t.umblr.com/redirect?z=http%3A%2F%2Fwww.academia.edu%2F19607959%2FTaphonomic_Bone_Staining_and_Color_Changes_in_Forensic_Contexts&t=YzYzM2ZhZDk1MjYzMzA1MjcyMmNlYzJhMThjMWY4ZTc3MDllOWI2OCxoV3BKSUI4Mw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181230179984%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) (from organic matter in the soil) can turn bones black. Furthermore, mercury can stain bones grey/silver to black.

Many fossils, too, can have black bones. [Black Beauty](https://t.umblr.com/redirect?z=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSpecimens_of_Tyrannosaurus%23%2522Black_Beauty%2522%3A_RTMP_81.6.1&t=OGM3MjllZDMxOGFjNmFhNjFjMmVjNDdkZTNlNzQ0ZGIwOWMzYTRiYixoV3BKSUI4Mw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181230179984%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1), a famous Tyrannosaurus specimen, has shiny dark bones due to minerals in the surrounding rock during fossilization.

* * *

  1. Despite the title, the site is not salacious. (though the morbid in-progress taxidermy might disturb employers anyway) [↩︎](https://argentdandelion.tumblr.com/post/181230179984/a-rainbow-of-bones-resource-on-skeleton-monster#fnref:1)


	3. Red, Orange, Purple, Blue

_(Note: The images here are just cartoony femurs illustrating colors, but the sources might be slightly grisly.)_

* * *

White, grey and yellow(ish) are the most common skeleton colors in both real life and fictional depictions, _Undertale_’s Sans and Papyrus included. Skeletons with brown or black bones are less common, but still have plenty of examples.   
Red, orange, pink, purple, blue, and green, however, are much rarer.

* * *

**Natural (But Weird) Colors**

(For people who like precise color data: Fox squirrel bone [source](https://t.umblr.com/redirect?z=https%3A%2F%2Fvmnhpaleontology.wordpress.com%2F2012%2F02%2F29%2Fsquirrel%2F&t=NzRlODVjY2I4NGE4MWQ0NzM2MzE4ZWZjYWVhM2EzNzgzYmYwMjNmYixZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) (sixth picture down), garfish [source](https://t.umblr.com/redirect?z=http%3A%2F%2Feruvanyo-food.blogspot.com%2F2011%2F06%2Fgarfish.html&t=ZDA2Y2I0YjkwMDI5NmU2YWVjNTAxNDQ1ODJhMzY4ZWRmNjg1NjVhNyxZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) (sixth picture down), Guishan redbone goat [source](https://t.umblr.com/redirect?z=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FRed-boned-and-common-goats-a-Red-boned-goat-b-Common-goat-c-The-teeth-of-a_fig9_225059688&t=NDNiZjg1OGM0MzM4YWU4NTVjNDJiZjBlYmFhZGNjYzM3MWMyZDAxMixZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1))

The bones of some animals are naturally very strange colors. Some Guishan goats of China’s Yunnan province have red bones, for no clear reason. The genetic disorder porphyria can make bones, including teeth, yellowish-orange or even red.[1](https://argentdandelion.tumblr.com/post/181500668936/a-rainbow-of-bones-resource-on-skeleton-monster#fn:1) While porphyria is a rare condition with several bad effects in humans, eastern fox squirrels _(above, left)_ all have porphyria, to no ill effect.

Garfish and eelpout both have bluish-green bones, and the Samkos bush frog has turquoise bones. A species of skink (a kind of lizard) and frog both have green bones, for the same reason: high levels of biliverdin, a breakdown product of hemoglobin. (Incidentally, excess bilirubin causes human infants to get green teeth.)

* * *

**Unusual Biological Circumstances**

Madder-Stained Bone [Source](https://t.umblr.com/redirect?z=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FRight-mandible-of-a-pig-stained-with-madder-prepared-in-1923-and-preserved-in-normal-salt_fig1_14171373&t=Mzg3NDY0MjM4NGFmM2Y4OTI3MWI4Njc3NjdkNDEyZjAzMmFhZTVkNixZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1), Sea Otter Teeth, Sea Otter Skull (for comparison)

Pigs fed madder root, used for dying things red, develop a red tinge to their bones. Similarly, a lifelong diet of sea urchins makes sea otters’ bones and especially their teeth and skulls purple-tinted, due to a strong purple pigment in the urchins.

* * *

**Funereal and Taphonomic Processes**

Ocher [source](https://t.umblr.com/redirect?z=https%3A%2F%2Fbonesdontlie.wordpress.com%2F2011%2F10%2F06%2Fcolored-bones-varied-meanings%2F&t=MjljNDBlMTE0ZDE3ODE3OTU5ZDlmOTc4ZmI4OTA5MWU4NmNlMmZjZCxZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1), Red Queen Bone [source](https://t.umblr.com/redirect?z=http%3A%2F%2Fspartanideas.msu.edu%2F2014%2F05%2F22%2Finvestigating-red-colored-bones-in-mesoamerica%2F&t=MzliMmQ4NWIxNDgyMjYyZTk3NWY0NzIyMDA2YWU0NTgzNTAxOWVmNixZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1), Calcined Bone [source](https://t.umblr.com/redirect?z=https%3A%2F%2Fjournals.plos.org%2Fplosone%2Farticle%3Fid%3D10.1371%2Fjournal.pone.0134429&t=MWNiZmFjNjE2NDRmYWRmZDkyZjg4ZDAyZmNjMTViY2EwNmQyYmRkZixZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1), Vivianite [source](https://t.umblr.com/redirect?z=https%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0379073815005447&t=NzY5YzcwMzUyZmMyMTFkY2Q4MzVhYWM4YzAzODE5YjhmZGRkMzZjOCxZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1), Copper stain [source](https://t.umblr.com/redirect?z=https%3A%2F%2Fbonesdontlie.wordpress.com%2F2011%2F10%2F06%2Fcolored-bones-varied-meanings%2F&t=MjljNDBlMTE0ZDE3ODE3OTU5ZDlmOTc4ZmI4OTA5MWU4NmNlMmZjZCxZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1), odontolite [source](https://t.umblr.com/redirect?z=http%3A%2F%2Fthe-earth-story.com%2Fpost%2F152248032398%2Fodontolite-also-known-as-bone-turquoise-this&t=OTg1ZDliMDRjOTkyMTkyYTM0MWMwYjUzMWI2NzgwMzdmYzg1MmM4ZixZNnJuejliZw%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181500668936%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) (middle picture, below).

The reddish-brown pigment ocher was common in ancient funereal practices. As the body decayed, the ocher on it tinted the bones orangeish-brown (or, arguably, dull red).

However, some human skeletons have a more intense red hue. Some ancient Mesoamerican (e.g., Mayan) remains are intensely red due to cinnabar, a mercury compound once used as a red pigment. Unlike ocher, the entire bone, not just the surface, is stained red. One explanation for this is that dishes painted with cinnabar led to cinnabar getting into their food, staining their bones. (and surely causing horrible mercury poisoning)

While manganese dioxide (mentioned in Part 1) causes black stains, manganese carbonates cause pink to reddish-brown stains. Permaganate ions can also stain bones purple.

When it comes to shades of blue, green and in between, there are several factors. Copper and copper alloys (e.g., bronze), can stain bones a bluish-green color much like that of the Statue of Liberty. Bones can also turn a blue color if heated. Indeed, fossilized dentine (tooth mineral) from mastodons, similar to woolly mammoths, turns such a lovely shade of turquoise when heated it was sold as the gemstone odontolite. Sometimes, bones are found with bluish tints for unclear reasons; apparently the dung of lizards and bats in caves is a factor.

People on Tumblr who love crystals will be happy to know about vivianite. In certain conditions, the mineral grows crystals on skeletons and turns them partly blue/blue-green. Algae, too, grows on bones, staining them green.

* * *

  1. A different phenomenon from orange beaver teeth, which are colored by iron: no animals the author knows of naturally have similarly-colored orange skeletons. [↩︎](https://argentdandelion.tumblr.com/post/181500668936/a-rainbow-of-bones-resource-on-skeleton-monster#fnref:1)


	4. Glowing and Glittering

_Left:_ No suitable photographs of glowing human bones exist; this approximation is based on human bone descriptions and chameleon bones _(description below)_   
_Right:_ Approximation of bone with porphyria, under a focused blacklight. _(description below)_

It’s pretty popular to depict Sans (and, to a lesser extent, Papyrus) as emitting some colorful glow, whether it’s a flashing eye or “ectoplasm flesh” there’s no evidence for them having.

But the idea of “ectoplasm flesh” isn’t necessary to portray them with an appealing glow. Bones already glow in real life: just not in a way that’s normally visible to the human eye.

First, an explanation is in order. [Fluorescence](https://t.umblr.com/redirect?z=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FFluorescence&t=OGU2MjZmYjIwNDA3NmYzYjVjYjFhODdmNGQ5Zjg2NWQ4NmZmZGI2NCw3bGJ4a2tINg%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181625325841%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) is a phenomenon in which substances absorb light and then re-emit it in another wavelength (color). The most famous example of this is when the absorbed light range comes from the ultraviolet region of the light spectrum, which is invisible to human eyes, and the emitted light is in the visible region. This gives the fluorescent object a distinct color that can be seen when exposed to UV light, like a blacklight.

* * *

#  **Glowing**

Assuming skeleton monster bones are like human ones unless otherwise stated, Sans lovers will be happy to know human bones’ [pale blue glow](https://t.umblr.com/redirect?z=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DmiBjDwAAQBAJ%26q%3Dpale%2Bblue%23v%3Dsnippet%26q%3Dpale%2520blue%26f%3Dfalse&t=MTdjNjk2MDI5MTQ0ZWQ1Nzc1NmRmYTgxNGNhOTY4MWU1OTgwODFmZiw3bGJ4a2tINg%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181625325841%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) under blacklight is similar to that of common Sans “ectoplasm-flesh”. (though surely weaker)

  
Approximation of human bone stained by tetracycline, viewed under ultraviolet.

The fluorescence varies, too. The antibiotic tetracyline (mentioned [earlier](http://argentdandelion.tumblr.com/post/181029039127/a-rainbow-of-bones-resource-on-skeleton-monster)) stains bones a yellowish color not only in visible light, but ultraviolet too: bones with tetracycline glow a brilliant yellowish-gold or yellowish-green. (descriptions vary; above is yellowish-green)

Furthermore, for both human and animal bones, the fluorescent glow changes from blue to yellow (various shades have been observed) and [becomes weaker](https://t.umblr.com/redirect?z=https%3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2Fs00414-017-1546-1&t=Njk0MWYwZjUyODU4NzA0OTI2ZjU1NjE4NzkyMDk2MTZhMmE4YzA2Myw3bGJ4a2tINg%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181625325841%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1) with increasing time since death. Skeletons with porphyria (mentioned in [Part 3](http://argentdandelion.tumblr.com/post/181500668936/a-rainbow-of-bones-resource-on-skeleton-monster)), such as those of eastern fox squirrels, glow impressively pink under blacklight. Chameleons are even stranger: with the right equipment, it’s possible to see chameleons’ fluorescent bluish bones even through their skin.

* * *

#  **Glittering**

  
Approximation: Most items claiming to be pyritized bones are technically marcasite, which isn’t as pretty, and most of the pretty specimens are ammonites, which are shells and not bones.

Speaking of fluorescence and minerals, there’s a perfect blend of the two: fossil bones.

Through the fossil process of petrification, living material is replaced with minerals. In two kinds of petrification, ancient bones can be turned into replicas made of opal (yes, the gemstone) or iron pyrite/marcasite. (the minerals are related and sometimes conflated with each other)

Interestingly, fossils with bits of iron pyrite can suffer from “[pyrite disease](https://t.umblr.com/redirect?z=https%3A%2F%2Fwww.smithsonianmag.com%2Fblogs%2Fnational-museum-of-natural-history%2F2018%2F08%2F10%2Felegy-hatcher-triceratops%2F&t=MGRiNDQ0MTg3Mjk5ZDlkYjZhNTU4Y2EzNzEyOWZiOGQwMjQ3OTlkNCw3bGJ4a2tINg%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181625325841%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1)” in humid air: as the disease progresses, the fossil crumbles and turns to [dust](https://t.umblr.com/redirect?z=https%3A%2F%2Fdepositsmag.com%2F2018%2F06%2F26%2Fthe-trouble-with-pyrite%2F&t=N2QwYTY4NGMzMjczNDgxZGFmOWFjNzEzNGE3MWJlNjIzOTczMWVkYiw3bGJ4a2tINg%3D%3D&b=t%3AHZZTbr56CX-Pu8cYzedJTw&p=https%3A%2F%2Fargentdandelion.tumblr.com%2Fpost%2F181625325841%2Fa-rainbow-of-bones-resource-on-skeleton-monster&m=1).[1](https://argentdandelion.tumblr.com/post/181625325841/a-rainbow-of-bones-resource-on-skeleton-monster#fn:1)

* * *

  1. I mention this because the delicate status of pyritized bones and the fact they can eventually turn to dust parallels a common theme of Sans-focused works. [↩︎](https://argentdandelion.tumblr.com/post/181625325841/a-rainbow-of-bones-resource-on-skeleton-monster#fnref:1)


	5. Practical Applications & Conclusion

This series has covered a lot of fun facts, but what are the practical applications?

* * *

**General Character Design**

Firstly, the series’ information might help in character differentiation. Though Sans’ and Papyrus’ bones are the same chalk-white color in-game, it’s nonetheless common to give them different colors. Beyond differentiating the two further, it’s likely artists do this as other colors are more interesting and easier to shade than pure white, so the bone colors mentioned here might be useful for this.

The Undertale fandom may find tips on character differentiation especially useful, as so many skeleton monster characters look alike. (That said, many characters are alternate-universe versions of Sans and Papyrus, so their appearances are inherently constrained) Choosing an unusual color, beyond just being cool to look at, might help in making a design conspicuously unique.

As the Snowdin Shopkeeper and innkeeper sister’ drastically different colors suggest, monster siblings are not necessarily close in color. Yet, if similar colors are expected, the fact some skeleton colors (e.g., red, brown) have multiple variants or similar colors may be handy for a desired level of similarity.

* * *

**Hybrid Fanchildren and Non-Humanoid Skeletons**

Speaking of character design, hybrid fanchildren are pretty common. Certain trends are common in skeleton fanchildren, such as the child having the same bone color as the parent. Why not instead mix colors from the parents? After all, bones indeed come in different colors, and real-life hybrids like ligers and zorses do have mixtures of parents’ coat colors and patterns.

Why not add something less obvious, too? Since Guishan goats have red bones, why not make a goatlike (e.g. Boss Monster) skeleton red? Or a skeleton hybrid with one fish-like, or frog-like, or lizard-like parent have green or turquoise bones? Why not make an otter-like skeleton have purplish bones, like sea otters, or a chickenlike monster have black bones?

* * *

**Color Coding for Magic or Other Themes**

  
  
In video games and other media, monsters are often color-coded according to their abilities; for example, Fire-type Pokémon are often red, orange, or yellow. Thus, a skeleton character with those colors would easily convey an association with fire. (especially applicable if it’s a fire monster hybrid)

In addition, bright green skeletons might be good for associations with radioactivity, poison, or radiant abilities, and skeletons with vivianite or calcite crystals might have sparkly or crystal-based abilities.

Related to this is porphyria: some works (e.g., **The Anomaly**, **Undertale Yellow**) show the Underground with monsters based on humanoid monsters such as vampires or werewolves. As porphyria is called “the vampire disease”, a skeleton that’s orange or dark red because of porphyria would link well to vampires. (_below)_

* * *

**Sickness and Association with Poison**

“Sick fics” are a pretty popular genre of fanfiction. Certain drugs or poisons can change bones’ color. Certain antibiotics (e.g., tetracycline) and the heavy metal cadmium can turn bones yellow. Mercury turns bones grey. Cinnabar, a compound of mercury, can turn bones bright red from great enough exposure, and at that level of exposure there would surely be symptoms of mercury poisoning, such as delirium.

* * *

**Glowing Bones**

Since glowing skeletons are pretty popular in _Undertal_e, why not consider the real phenomenon of bones glowing under ultraviolet light? Subtle differences in UV light might lead to a medical mystery from an assumed illness. Tetracycline changes bones’ color under UV just as in visible light, and fox squirrels’ porphyria causes a pink glow.

* * *

**Conclusion and Caveat**

The monsters of _Undertale_ have the convenient excuse of being “made of magic”, and thus potentially avoiding biological rules. So, if the author can’t find examples of, say, pink or bright purple skeletons, this doesn’t have to restrict character design. Yet, some authors prefer drawing _Undertale_ characters with a measure of realism, or borrowing real-world science to flesh out (if you’ll excuse the pun) the lives of monsters. For example, Undyne never mentions being able to breathe underwater and whether she has gills is ambiguous, but it’s a common detail nonetheless because of how fishlike she is.

In any case, the series’ many examples of color might be useful even for those who don’t care about real-world biology, simply by opening their eyes to a rainbow of bones.

* * *

**Related Reading:**  
**_[Tips on Skeleton Design](http://argentdandelion.tumblr.com/tagged/Tips-on-Skeleton-Design/chrono/)_**(Tips on designing skeleton characters and trends in the Undertale fandom)  
**_[Adult Chara Consistency: Similarities in Design of an Adult Chara](http://argentdandelion.tumblr.com/post/179600892071/adult-chara-consistency-similarities-in-design-of)_** (Analysis of artistic commonalities between depictions of Chara and also Asriel as adults)  
**_[Papyrus is Probably a Better Boyfriend than Sans](http://argentdandelion.tumblr.com/tagged/Papyrus-is-Probably-a-Better-Boyfriend-Than-Sans/chrono/) (especially [Part 3](http://argentdandelion.tumblr.com/post/176747022689/papyrus-is-probably-a-better-boyfriend-than-sans))_** (scientific analysis of why Papyrus is probably a better boyfriend than Sans by the tastes of most women, most of the time)


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